I want to wire up a toggle switch so that it will blow a particular fuse when flipped.
It is an automotive fuse that is being used by other systems on the vehicle so it needs to work perfectly fine until the switch is triggered.
What’s the easiest way to do this?
Connect switch so that it is a dead short when switched to the on position and wire in series with the particular circuit. Something like so
+Bat ------ fuse ------- switch ----- -Battery (ground)
What you want is a SPST switch which will have two connections, wire one to the fuse side and the other to the ground side of the circuit. Make sure it is of sufficient rating to handle a dead short (lots of current) for whatever time frame your particular fuse takes to blow (of special important for slow-blow type_.
I would make sure the switch and wiring is rated for more current then the fuse is and then simply wire the switch to the fuse and to a good ground point.
^yep, what he said.
It’s critically important that you put the switch on the side of the fuse that is NOT the battery side.
Get this wrong and you will melt part of your wiring harness. Which will not be fun to fix.
Simple and obvious… I should have thought of that.
I’m wiring up a nearly theft-proof system which will require the driver to hold a momentary toggle in a location that’s “hidden in plain sight” but looks totally factory in order for the ignition to work.
If a thief tries to start the vehicle without holding the toggle, the horn will sound. I’m going to wire in a normal toggle switch on the dash as a decoy that, when flipped, will blow the fuse for the ignition and make it impossible to start the vehicle without replacing the fuse. That way, if the thief is savvy and tries to circumvent the kill switch, he will destroy any chance he had at success.
If you are needing to ask the forum how to wire up a dead short, you may want to run the schematic of your plan by someone with some electronic skills so that you don’t end up shorting out your ECU, or starting your car on fire.
A latching relay in the ignition circuit would be a much better idea than ‘blowing a fuse’.
A more eloquent solution would be a wireless key fob that when the button is pushed, it triggers a relay that enables the starter circuit for enough time for you to start the car.
That way, should someone jiggle the ignition on your car, or try to hot wire it from inside the vehicle, they wouldn’t be successful because your starter circuit interrupt would be under the hood in line with the starter relay.
Jeremy,
Paul is right - and in fact you can get a resettable circuit breaker that is hidden up in under the dash. I used one for a while when I had an intermittent short that kept eating fuses. Just be sure whatever you do, do it solid. Every added component increases the risk that YOU won’t be able to start the car when you need to, and it will happen on a dark night in the pouring rain without a flashlight.
Also, there is no such thing as theft proof - only more theft resistant. A determined enough thief can just get it towed.
JAG “Grand Theft Manual” MAN
Something like this, wired to a more heavy duty automotive relay wired in-line with the wire going to your starter relay…Pushing the button while turning the ignition key would complete the circuit and allow the car to start. No need for fake switches as there would be no physical switch for a ‘thief’ to be able to use.
That’s a neat solution but I don’t like the idea of having 2 key fobs (1 for door locks and 1 for ignition).
What about wiring in a relay that’s activated by the keyless entry actuator? Unless the door is unlocked with the key fob, the starter won’t work.
Of course, if the door lock actuator or the key fob dies, I’d be stuck.
I’m thinking out loud with that idea…
But you know where the remote 12v switch is wired in under the hood, and could bypass it with a few minutes of work. A criminal won’t spend the time to do that. They’re looking for easy jobs, not something they have to monkey with (and possibly be discovered).
What about a reed switch? It can be hidden & used with a magnet.
Connect a relay off the glove box light switch so that you have to have the glove box open for the starter relay to energize. 
Or connect an arduino off of the glove box light switch so that you have to open and close the glove box X times before the relay will engage the starter relay circuit.
I could do that with the center console lid since it’s easier to get to from the driver’s seat… hmmmm.
I really dig the idea of running the relay off of your power antenna feed…so the radio has to be on for the car to start…the only problem is that if you leave the radio on all the time, it defeats the system.
Uber slick would be to have two relays in series, one powered by the vehicle headlights, then the other powered by the radio antenna power feed so that you have to have the headlights on, and the radio on, before the starter circuit will work.
Once upon a time, I had a Chevy truck that required you to turn the parking lamps on before it would start. If you didn’t turn on the parking lamps, the ignition switch honked the horn. The system was installed by the previous owner and it was always fun to watch friends try to start my truck. That’s where I got the idea but I was reading up on some of the forums and most experienced car thieves know the usual tricks for ignition kill switches… that’s why I want to come up with something more difficult to figure out.
Paul, you have me thinking about all sorts of cool ideas now…
The more complicated and “reach-aroundy” the starting process is, the more people will start asking questions. Call me paranoid but considering the value of the cargo I’ll have from time to time, I’d rather not have loose lips sinking my ship, as it were. I think something integrated to look completely nonchalant will be the best solution.
I was reading one forum and, apparently, many police cars are fitted with a brake pedal disconnect of some sort that allows the officer to leave the car running without worrying about theft. Pressing the brake pedal doesn’t allow you to shift out of park without the proper switch being flipped, supposedly. That would be a pretty cool option, as well.